Peroxometal-mediated environmentally favorable route to brominating
agents and protocols for bromination of organics*
Upasana Bora**, Mihir K. Chaudhuri, Deepa Dey, and Siddhartha S. Dhar
Department of Chemistry, Indian Institute of Technology
Guwahati, Guwahati-781039, India
Abstract: Higher-valent transition metals react with H2O2
to form peroxometallates, thereby activating the coordinated peroxide.
Based on the reaction profiles of peroxometal species, environmentally
acceptable newer syntheses of tetrabutylammonium tribromide (TBATB),
Bu4NBr3, cetyltrimethylammonium tribromide (CTMATB),
cetyl(Me)3NBr3, and tetraethyl-ammonium tribromide
(TEATB), Et4NBr3, have been developed from the
reactions of the corresponding quaternary ammonium bromides with H2O2
and a catalytic amount of vanadium(V) or molybdenum(VI). Other transition
metals capable of activating peroxide give similar results. The quaternary
ammonium tribromides (QATBs) thus produced, especially TBATB and CTMATB,
very efficiently act as clean and selective brominating agents for a
variety of organic substrates. Very facile bromination of organic substrates,
including aromatics, is also possible by tetrabutylammonium bromide
(TBAB) Bu4NBr, either promoted by V2O5H2O
2 or catalyzed by MoO42H2
O2. The scope of the protocols has been underscored, and
the relevance to green chemistry has been highlighted.
* Lectures presented at the International Symposium
on Green Chemistry, Delhi, India, 10-13 January 2001. Other presentations
are published in this issue, pp. 77-203.
** Corresponding author.